1. Field of the Invention
The present invention relates to a bi-axial test apparatus which permits testing samples of geomaterials under axial loads while continuously monitoring the axial force, axial and lateral displacement and translation of a base supporting the sample.
2. Description of the Prior Art
Bi-axial testing of geomaterial, which, for purposes of this application, is defined as including, but not limited to soil, sand, rock, ceramics, concrete, snow and ice, has been recognized as important in determination of geomaterial characteristics. Bi-axial testing has been carried out in the prior art, as reported by I. Vardoulakis and M. Goldscheider in a publication entitled "Biaxial Apparatus for Testing Shear Bands in Soils", presented at a conference in Stockholm in 1981. (I. Vardoulakis and M. Goldscheider (1981). Biaxial Apparatus for Testing Shear Bands in Soils. X ICSMFE, Stockholm, 4/61, 819-824).
The experimental apparatus disclosed therein utilized a specimen support plate that was mounted on rollers, as is shown in FIG. 5 of the publication, and wherein the loads were applied by an axial piston force acting on the soil sample in a longitudinal direction, while the sample was permitted to shear and laterally displace in one axis as it was loaded. The sample or specimen was enclosed in a rubber membrane. Eccentric loading and friction, particularly in relation to the mounting of the specimen support base, and the inability to determine displacement along the axial length of the specimen as it was being loaded limited its applicability.
Various tri-axial test devices have been advanced and also are well known. It also is known to encase geomaterial samples in outer membranes and surround the sample with a fluid under a desired hydrostatic pressure in a chamber during the loading. Such a device, in simplifed form, is shown in U.S. Pat. No. 3,616,685. The device shown in the above-identified Vardoulakis article also included an outer confining pressure housing. Generally, in tri-axial testing of samples the lateral pressures generated by axial loads in the specimen are of interest. U.S. Pat. Nos. 4,047,425; 4,599,891; and 4,122,704 illustrate such devices.